1. Field of the Invention
The present invention relates to a technique for simultaneously forming irregularity in a surface of a reflecting electrode and contact holes in an interlayer insulating film formed on a silicon film, in which sources and drains of TFTs are formed, above the sources or drains in a process for manufacturing a reflective liquid crystal display device, to shorten the manufacturing process.
2. Description of the Related Art
In a conventional active matrix reflective liquid crystal display device in which each of pixel electrodes comprises a reflecting electrode serving as a reflecting scattering plate by surface irregularity, a driving-side TFT substrate is manufactured as shown in FIG. 13. FIG. 13 shows a manufacturing process for a liquid crystal device having a pixel structure comprising bottom gate structure TFTs. However, a pixel structure comprising top gate structure TFTs can also be manufactured by basically the same process.
First, as shown in FIG. 13A, a metal film is deposited on a transparent substrate 1, and then dry-etched by photolithography to form gates G and auxiliary capacitance electrodes Cs. Then, a gate insulating film 2 is deposited, and a polysilicon film 3 is further formed thereon.
Next, in order to prevent impurity injection into channel regions during impurity doping of source and drain regions, stoppers 4 are respectively formed on portions of the polysilicon film 3 corresponding to the channel regions in self-alignment with the gates G, followed by impurity doping of the source and drain regions.
Then, the polysilicon film 3 is separated into islands by photoresist step and etching step to form low-temperature polysilicon thin film transistors (TFTs).
Next, an interlayer insulating film 5 is formed (FIG. 13B). In order to form contact holes in the interlayer insulating film 5, a photoresist layer 6 is first formed on the interlayer insulating film 5, and then patterned by photolithography using a patterned mask as a photomask in which apertures are formed in portions corresponding to the contact holes (FIG. 13C). Then, the interlayer insulating film 5 is etched by using the patterned photoresist layer 6 as an etching mask to form contact holes H1 in the interlayer insulating film 5 (FIG. 13D).
Next, a metal film is deposited by sputtering or the like, and then etched to form source electrodes S1 connected to sources S of the TFTs through the contact holes H1, signal wiring, and drain electrodes D1 connected to drains D of the TFTs through the contact holes H1 (FIG. 13E).
Next, an irregular shape as a base for forming surface irregularity in a reflecting electrode having a reflecting scattering ability is formed by using two layers each comprising a photoresist material as follows. First, a first layer 7 for forming the basic structure of the irregular shape is formed by photolithography using a photoresist material (FIG. 13F). The photomask used in this step has second contact holes H2 communicating with the source electrodes S1 or the drain electrodes D1. Next, a second layer 8 for improving the reflecting property is formed by photolithography using the same photoresist material as the first layer 7 (FIG. 13G). The photomask used in this step has third contact holes H3 communicating with the drain electrodes D1. In this way, the surface irregular shape having a two-layer structure comprising the first and second layers 7 and 8 is formed.
Next, a metal film of Al, Ag, or the like, which has high reflectance, is deposited, and then subjected to photolithography to form a reflecting electrode 10 (FIG. 13H).
In this way, the driving-side TFT substrate is completed. An alignment film is coated on each of the TFT substrate and a counter substrate on which a color filter and a counter transparent electrode are formed, and then subjected to alignment. Then, both substrates are bonded together with a sealing material by using a gap material for keeping an appropriate gap between both substrates, and a liquid crystal is injected into the gap, followed by sealing to obtain a liquid crystal display panel.
The method of manufacturing a driving-side TFT substrate of a conventional active matrix reflective liquid crystal display device shown in FIG. 13 requires the steps of respectively forming the first and second layers 7 and 8 each comprising a photoresist material and then patterning the layers by photolithography to provide the reflecting electrode 10 with the predetermined irregular surface shape. Therefore, a total of three insulating layers including the interlayer insulating film 5 is finally formed between the silicon film, in which the sources S and drains D of TFTs are formed, and the reflecting electrode 10. Also, the method comprises the separate steps of forming the source electrodes S1 and the drain electrodes D1, and forming the reflecting electrode 10, to cause the problem of increasing the number of the steps, thereby increasing the manufacturing cost.